Hi,
I have used gpu's both for gaming and for photo editing, and I think i may be able to help. Most if not all gaming cards are 8bit color cards, they are excellent for gaming, but they do not provide 10bit color for things like photoshop or CAD. Gaming cards like the AMD HD6000's or HD7000's do not support 10 bit color. If you want 10 bit color you need to get a special workstation card, like an nvidia Quadro, or Amd Firepro. I myself currently have a Quadro 600 and it supports 10 bit color. I tried some gaming on the card, and it works too, i can play Crysis on medium-low settings, with decent frame rates. Quadro cards are based on nvidia's gaming cards except they are optimized for workstations, and they have different drivers, etc. So if you want 48bit as you call it, you will need to go for either a Quadro or a Firepro GPU. What is your budget for one, I can help you chose, I just need to know the budget, and what you need it for. Also yes, these cards are directX 11.
Also note:
1. You need a 10bit monitor with display port (other connections dont have 10bit color, unless you have HDMI with deep color)
2. You need a 10 bit capable GPU, like a quadro
*Note professional displays ie. for photo editing use 10 bit (48 bit color), regular use 8, so i think this is what you mean by 48bit.
Hope this helps!